1. Field of the Invention
The present invention relates to an image transfer method and an image transfer system, and also to an image signal output apparatus and a terminal used therefor.
2. Description of the Related Art
In various fields such as medicine, images are conventionally displayed on an image display device such as a CRT display or output on a film by using a printer such as an LP (Laser Printer), after image data obtained by reading information of radiation images of subjects recorded on stimulable phosphor sheets or films are subjected to predetermined image processing.
Recently, digital image processing techniques using computers have been developed. Furthermore, various kinds of image generating apparatuses (image generating modalities) such as apparatuses for CT (Computed Tomography), MRI (Magnetic Resonance Imaging), and CR (Computed Radiography) using the digital image processing techniques have been spreading as apparatuses for generating diagnostic images and widely put into practice for diagnosing lesions and injuries, or for understanding the degrees thereof.
A CR apparatus is a radiation image recording and reading apparatus. In a CR apparatus, stimulable phosphor which stores partial energy of radiation irradiated thereon and emits light in accordance with the stored radiation energy when exposed to stimulating rays such as visible light or infrared rays is used. By using a stimulable phosphor sheet, radiation image information of a subject such as a human body is recorded thereon and an image signal is obtained by using photoelectric reading means such as a photomultiplier which photoelectrically reads the light emitted from the stimulable phosphor sheet by scanning the sheet with the stimulating rays. The CR apparatuses are in wide use and put into practice (for example, see Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)-11395, 55(1980)-163472, 56(1981)-104645 and 55(1980)-116340).
The assignee has proposed a method of photoelectrically reading the light from both sides of a stimulable phosphor sheet (for example, Japanese Unexamined Patent Publication Nos. 55(1980)-87970 and 8(1996)-116340). In this method, the photoelectric reading means described above are used on both sides of the stimulable phosphor sheet and the stimulating rays are irradiated on either one side or on both sides of the sheet in order to photoelectrically read the light emitted from both sides of the sheet.
In this double-sided light-collection reading method, a stimulable phosphor sheet is formed by disposing the stimulable phosphor on a surface of a transparent base material and the stimulable phosphor sheet storing a radiation image is placed on a transparent holder. The photoelectric reading means are located above and below the sheet. In other words, the photoelectric reading means placed above the holder reads light from the front side of the sheet while the photoelectric reading means placed below the holder reads light emitted from the backside of the sheet.
Image signals read from both sides (a front-side image signal and a rearside image signal) in the above manner are each subjected to filtering processing having different frequency characteristics. The signals are then added at corresponding pixels on both sides, and an addition image signal (superposition image signal) is obtained. According to this addition image signal, high frequency noise occurring randomly in each of the signals is smoothed by the addition. Moreover, since the light is collected from both sides of the sheet, light collection efficiency is improved and a superposition image displayed based on the superposition image signal has an improved S/N ratio, which leads to an image that is easier to see.
Furthermore, as a method of obtaining radiation image information by using the stimulable phosphor sheet described above, a method of obtaining a radiation image having a specific subject portion emphasized or extracted has been known. In this method, a plurality of image signals are obtained by reading a plurality of radiation images photographed and recorded in different conditions, and an image corresponding to a subtraction of these images, that is, the radiation image having a specific portion emphasized or extracted is obtained by finding a subtraction image signal based on a subtraction operation on these images. As this subtraction processing (operation), time subtraction processing and energy subtraction processing disclosed in Japanese Unexamined Patent Publication Nos. 7(1995)-3704 and 8(1996)-76741 are basically known, and the assignee has also proposed time subtraction processing using a stimulable phosphor sheet described in Japanese Unexamined Patent Publication No. 60(1985)-206392 and energy subtraction processing using a stimulable phosphor sheet described in Japanese Unexamined Patent Publication Nos. 59(1984)-83486 and 60(1985)-225541, for example.
Meanwhile, due to the spread and progress of networking technologies following the recent development of technologies in communications and computers, diagnostic medical image networks have been installed as image transfer systems in the field of medicine, for example. In such a network, various kinds of image generating apparatuses installed in a medical examination room or the like of a hospital are connected to an image display apparatus or an image output apparatus such as a printer installed in a consulting room or a laboratory, and diagnostic image information obtained by the image generating apparatuses in the examination room can be obtained even in the consulting room.
In such an image transfer system using the network or the like, in the case where an image after an operation such as the addition operation or the subtraction operation described above is output from an image output apparatus, an addition image signal or a subtraction image signal after the operation is conventionally transferred from the image generating apparatus to the image output apparatus, and the image output apparatus outputs the image based on the transferred image signal.
However, in this method, it is difficult for the output image to be output again after being subjected to a further addition or subtraction operation using a different parameter, following confirmation of the output image.
In order to solve this problem, a method of outputting an image based on an image signal after an operation is possible. In this method, a plurality of image signals obtained by an image generating apparatus, that is, original image signals are transferred as they are from the image generating apparatus to an image output apparatus, and the image output apparatus carries out the addition operation or the subtraction operation described above using a predetermined parameter on the original image signals having been transferred. An image is then output based on the image signal after the operation. Alternatively, another method of image display is also possible. In this method, the original image signals are transferred together with an addition image signal or a subtraction image signal after an operation, and an image is normally displayed based on the addition image signal or the subtraction image signal. In the case where parameter change is necessary, an image is displayed based on a signal after the operation using the original image signals.
However, if a plurality of image signals for one image are transferred, the amount of data transfer increases and transfer time becomes longer or a large-capacity storing device for storing the large amount of data becomes necessary.
The present invention has been conceived based on the above considerations. An object of the present invention is therefore to provide an image transfer method and an image transfer system enabling reduction in the amount of data and an image signal output apparatus and a terminal used therefor, in the case where a plurality of image signals are transferred so that an image output apparatus can output an image after carrying out an addition operation or a subtraction operation while changing an operation parameter.
An image transfer method of the present invention pays attention to a characteristic that a plurality of original image signals obtained by a radiation image information reading apparatus described above have different frequency characteristics and noise characteristics but have substantially similar values and the amount of data of a subtraction signal is less than the amount of the original image data.
In other words, a first image transfer method of the present invention is a method of transferring an image in an image transfer system comprising an image signal output apparatus for outputting an image signal representing a radiation image, a terminal for receiving the image signal transferred thereto, and transfer means for transferring the image signal output from the image signal output apparatus to the terminal. The image transfer to method comprises the steps of:
finding a subtraction signal between two image signals representing the radiation image;
transferring the subtraction signal together with either one of the two image signals from the image signal output apparatus to the terminal; and
restoring the image signal not having been transferred by using the subtraction signal and the image signal having been transferred. xe2x80x9cRestoring the signal not having been transferredxe2x80x9d refers to the following cases. Let one of the two image signals be A and the other B. If the image signal after an operation is an addition image signal C (C=Axe2x80x2+Bxe2x80x2) and if the signal A and a subtraction signal D (D=Axe2x88x92B) are transferred, the signal B is restored by an operation Axe2x88x92D=Axe2x88x92(Axe2x88x92B)=B. Here, Axe2x80x2 and Bxe2x80x2 refer to image signals after filtering processing having different frequency characteristics on the signals A and B respectively. Alternatively, in the case where the signal B and the subtraction signal D are transferred, the signal A is restored by an operation B+D=B+(Axe2x88x92B)=A.
A second image transfer method of the present invention is a method used in an image transfer system comprising an image signal output apparatus for outputting an image signal representing a radiation image, a terminal for receiving the image signal transferred thereto, and transfer means for transferring the image signal output from the image signal output apparatus to the terminal. The image transfer method comprises the steps of:
carrying out filtering processing having different frequency characteristics on two image signals representing the radiation image;
finding a processed image signal by carrying out an operation using two image signals after the filtering processing;
finding subtraction signals between the processed image signal and each of the two image signals;
transferring the two subtraction signals and the processed image signal from the image signal output apparatus to the terminal; and
restoring the two radiation image signals not having been transferred, by using the two subtraction signals and the processed image signal having been transferred. xe2x80x9cFinding subtraction signals between the processed image signal and each of the two image signalsxe2x80x9d refers to finding a subtraction signal E by carrying out an operation Axe2x88x92C=E and finding a subtraction signal F by carrying out an operation Bxe2x88x92C=F, with A, B meaning the two radiation image signals and C meaning an addition image signal as the processed image signal, as in the above example in the first method. Furthermore, xe2x80x9crestoring the two radiation image signals not having been transferredxe2x80x9d refers to restoration of the signal A by carrying out an operation C+E=C+(Axe2x88x92C)=A and restoration of the signal B by carrying out an operation C+F=C+(Bxe2x88x92C)=B. xe2x80x9cTransferringxe2x80x9d refers to transmitting at least two image signals from the image signal output apparatus to the terminal, and any method can be used for the transfer. For example, not only the transfer using the network described above but also a transfer via a medium such as a CD-R or an MO may be used. In this case, image data (image signals) are stored by using the image signal output apparatus as the medium, and the terminal reads the image data from the medium.
In the first image transfer method and in the second image transfer method of the present invention, it is preferable for the two image signals representing the radiation image to be two image signals representing images obtained by simultaneous photographing of one subject.
As the images obtained by simultaneous photographing, a radiation image represented by two image signals one of which represents a front-side image obtained by detecting light emitted from the front side of an image recording medium using stimulable phosphor and storing the radiation image and the other of which represents a rearside image obtained by detecting light emitted from the rear side of the image recording medium may be used, for example.
In this case, either the front-side image or the rearside image is a first image used in the superposition processing and the other is a second image used therein.
Alternatively, either the front-side image or the rearside image can be a low voltage image used in energy subtraction processing and the other can be a high voltage image used therein.
The front side and the rear side described above do not refer to specific surfaces of an image recording medium, and if one of the surfaces of an image recording medium is called the front side, the surface on the opposite side is called the rear side. Normally, the surface on the side being scanned by the stimulating rays is often called the front side.
In the first and second image transfer methods of the present invention, the two image signals representing a radiation image can be two image signals representing images obtained by photographing one subject at different times.
In this case, it is preferable for the two image signals representing the radiation image to represent images after positioning processing on the images obtained by photographing one subject at different times.
Furthermore, one of the image signals after positioning processing can be a present image used in time subtraction processing and the other can be a past image used therein.
The present and the past in the above explanation represent the order of photographing and do not refer to any specific time. In other words, between the images photographed at different times, the present image refers to an image photographed later (at a time closer to the present) than the other image, and the past image is an image photographed earlier (at a time going more backward to the past) than the present image.
A first image transfer system of the present invention is a system for realizing the first image transfer method of the present invention. In other words, the first image transfer system comprises an image signal output apparatus for outputting an image signal representing a radiation image, a terminal for receiving the image signal transferred thereto, and transfer means for transferring the image signal output from the image signal output apparatus to the terminal. In the system, the image signal output apparatus comprises subtraction signal generating means for generating a subtraction signal from two image signals representing the radiation image, and outputs the subtraction signal and either one of the two image signals, and the terminal comprises restoration means for restoring the other image signal not having been transferred, by using the subtraction signal and the image signal having been transferred thereto.
A second image transfer system of the present invention is a system for realizing the second image transfer method described above. In other words, the second image transfer system comprises an image signal output apparatus for outputting an image signal representing a radiation image, a terminal for receiving the image signal transferred thereto, and transfer means for transferring the image signal output from the image signal output apparatus to the terminal. In this system, the image signal output apparatus comprises signal processing means for carrying out filtering processing having different frequency characteristics on two image signals representing the radiation image, processed image signal generating means for generating a processed image signal obtained by using two image signals after the filtering processing, and subtraction signal generating means for generating subtraction signals between the processed image signal and each of the two image signals representing the radiation image, and the image signal output apparatus outputs the two subtraction signals and the processed image signal. Meanwhile, the terminal comprises restoration means for restoring the two radiation image signals not having been transferred, by using the two subtraction signals and the processed image signal having been transferred thereto.
In the image transfer systems of the present invention, it is preferable for the two image signals representing the radiation image to be two image signals representing images obtained by simultaneous photographing of one subject.
As the images obtained by simultaneous photographing, a radiation image represented by two image signals one of which represents a front-side image obtained by detecting light emitted from the front side of an image recording medium using stimulable phosphor and storing the radiation image and the other of which represents a rearside image obtained by detecting light emitted from the rear side of the image recording medium may be used, for example.
In this case, either the front-side image or the rearside image is a first image used in superposition processing and the other is a second image used therein.
Alternatively, either the front-side image or the rearside image can be a low voltage image used in energy subtraction processing and the other can be a high voltage image used therein.
In the image transfer systems of the present invention, the two image signals representing a radiation image can be two image signals representing images obtained by photographing one subject at different times.
In this case, it is preferable for the two image signals representing the radiation image to represent images after positioning processing on the images obtained by photographing one subject at different times.
Furthermore, one of the images after positioning processing may be a present image used in time subtraction processing while the other may a past image used therein.
A first image signal output apparatus of the present invention is an apparatus used in the first image transfer method and the system described above. The first image signal output apparatus comprises a subtraction signal generating means for generating a subtraction signal from two image signals representing a radiation image, and the first image signal output apparatus outputs the subtraction signal and either one of the image signals.
A second image signal output apparatus of the present invention is an apparatus used in the second image transfer method and system described above. The second image signal output apparatus comprises signal processing means for carrying out filtering processing having different frequency characteristics on two image signals representing a radiation image, processed image signal generating means for generating a processed image signal obtained by using two image signals after the filtering processing, and subtraction signal generating means for generating subtraction signals between the processed image signal and each of the two image signals, and the second image signal output apparatus outputs the two subtraction signals and the processed image signal.
A first terminal of the present invention is a terminal used in the first image transfer method and system described above. The first terminal comprises restoration means for restoring an image signal not having been transferred thereto, by using a subtraction signal of two image signals representing a radiation image and by using either one of the two image signals.
A second terminal of the present invention is a terminal used in the second image transfer method and system described above. The second terminal comprises restoration means for restoring two image signals representing a radiation image and not having been transferred thereto, by using a processed image signal obtained by an operation using two image signals after filtering processing having different frequency characteristics on the two image signals and by using two subtraction signals representing subtractions between each of the two image signals and the processed image signal.
In the image signal output apparatuses and terminals of the present invention, as in the image transfer methods and systems described above, it is also preferable for the two image signals representing the radiation image to represent images obtained by simultaneous photographing of one subject, such as a front-side image and a rearside image. In this case, the images can be used as first and second images for superposition processing or as a low voltage image and a high voltage image for energy subtraction processing.
Alternatively, as in the image transfer methods and systems described above, the two image signals representing the radiation image may represent images obtained by photographing one subject at different times. In this case, it is preferable for the two image signals to represent images after positioning processing, and the two images can be used as a present image and a past image used in time subtraction processing.
In the first image transfer method and system of the present invention, the image signal output apparatus generates the subtraction signal between the two image signals that are similar to each other, and the image signal output apparatus outputs the subtraction signal having been generated and either one of the image signals to the terminal. The amount of data of the subtraction signal is at least smaller than the amount of data of either a front-side image signal or a rearside image signal. Therefore, the amount of total data to be transferred is smaller in the present invention than in the case of simply transferring any two of the front-side image signal, the rearside image signal, and the processed image signal.
Meanwhile, in the second image transfer method and system of the present invention, the image signal output apparatus transfers to the terminal the processed image signal obtained by using the two image signals after the filtering processing having different frequency characteristics on the two image signals that are similar to each other and the two subtraction signals representing subtractions between each of the two image signals and the processed image signal. Therefore, the amount of total data to be transferred becomes smaller, as in the first image transfer method and system.
Therefore, according to the image transfer methods and systems of the present invention, upon transferring images obtained by simultaneous photographing of one subject, such as the first and second images used in the superposition processing or the low and high voltage images used in the energy subtraction processing, or upon transferring images obtained by photographing one subject at different times, such as the present and past images used in the time subtraction processing, transfer time for one image can be shortened, and fast transfer can be realized. At the same time, the capacity of a storing device for storing data can be smaller. In other words, the number of images which can be stored can be increased.
Furthermore, according to the first image transfer method and system of the present invention, the terminal restores the image signal not having been transferred thereto, by using the subtraction signal and the image signal having been transferred. Therefore, the processed image signal can be generated by using the restored image signal, and an image after changing a parameter for addition or subtraction operation can also be output.
Moreover, according to the second image transfer method and system of the present invention, the terminal restores the two image signals not having been transferred thereto, by using the processed image signal and the two subtraction signals. Therefore, as in the first image transfer method and system, the processed image signal can be generated by using the restored image signals, and an image after changing a parameter for the addition or subtraction operation can also be output.